Embodiments of disclosed technology relate to an array substrate and a method of manufacturing an array substrate, and a liquid crystal display.
Presently, liquid crystal displays (LCDs) are flat panel displays which are commonly used; thin film transistor liquid crystal displays (TFT-LCDs) are the main kind of liquid crystal displays. TFT-LCDs have been dominating the market of mediate and small sized displays, due to low cost, high yield and excellent display effect.
Fringe-field switching (FFS) technology can improve the picture quality of TFT-LCDs, and has advantages of wide viewing angle, high aperture ratio, short response time, no push Mura, and so on. However, the manufacturing process of a FFS mode LCD, electrical field formation and switching mode of liquid crystal and so on give rise to serious signal delay of common voltage (Vcom), and crosstalk occurs. Crosstalk is an important factor affecting picture quality, and may represent the degree of influence from a gray-scale picture in one region to an adjacent pixel region. The industry standard generally requires crosstalk of less than 2%.
In the liquid crystal displaying technology, capacitance formed between a common electrode and a pixel electrode is an important factor for the common electrode to generate signal delay, and the amount of the capacitance can refer to the calculating formula: C=εrε0*S/d, where C is capacitance; εr is relative dielectric constant, which is related to material property; ε0 is absolute dielectric constant; S is the area of the electrodes; and d is the distance between the electrodes.
FIG. 1 is a diagram of capacitance formed between a common electrode and a pixel electrode in FFS mode LCD, and FIG. 2 is a diagram of capacitance formed between a common electrode and a pixel electrode in TN mode LCD.
As shown in FIG. 1 and FIG. 2, the common electrode 13 is applied with a common voltage (Vcom) signal, and the pixel electrode 11 is applied with a pixel voltage (Vpixel) signal, and capacitance is formed between the common electrode 13 and the pixel electrode 11. In the FFS mode LCD, the common electrode 13 and the pixel electrode 11 are both located on an array substrate 50, and the capacitance dielectric material between the common electrode 13 and the pixel electrode 11 is a passivation layer (PVX), of which εr is about 5 and d is about 0.5 μm. As shown in FIG. 2, in the TN mode LCD, the common electrode 13 is located on a color film substrate 60, and the pixel electrode 11 is located on an array substrate 50, and the capacitance dielectric material between the common electrode 13 and the pixel electrode 11 is liquid crystal (LC), of which εr is about between and 12 and d is about 5 μm. Referring to the above formula, it can be estimated that the Ccom in the FFS mode is about ten times of that in the TN mode, and the capacitance formed between the common electrode and the pixel electrode in the FFS mode is increased by one order than that in the TN mode. Thus, compared with TN mode LCD, the loading ability of the common voltage of the FFS mode is relatively low, and crosstalk more easily occurs.
High aperture ratio FFS (HFFS) LCDs are one kind of FFS LCDs, which are mainly used for TFT-LCDs of mediate and small size. The typical structure of HFFS type array substrate comprises a base substrate, data lines and gate lines are formed to transversely and longitudinally cross to form a plurality of pixel units on the base substrate, and each of the pixel units may comprise a switching element, a pixel electrode and a common electrode having slits. The pixel electrodes arranged in a matrix are disposed to opposite to the common electrode of a whole piece, and the common electrode has slits in the each pixel unit. The region constituted by the pixel units is referred to a pixel region, and the region outside of the pixel region is referred to an interface region.
FIG. 3 is a diagram of the formation of electric field and rotation of liquid crystal in a conventional HFFS LCD. As shown in FIG. 3, the common electrode 13 and the pixel electrode 11 are both located on an array substrate, and they can both be formed of indium tin oxides (ITO). The common electrode 13 with slits and the underlying pixel electrode 11 together form a horizontal electric field 70 when applied a voltage therebetween. The electric field 70 can rotate the liquid crystal molecules, which are horizontally arranged between the array substrate 50 and the color film substrate 60, to function as a light valve. FIG. 4 is a diagram of hierarchy structure of a conventional HFFS LCD. As shown in FIG. 4, the sequence of deposition and etching of an HFFS LCD manufactured by using six-photolithography method may include: a gate line and the gate electrode (Gate), a gate insulation layer (GI), an active layer (Active), a pixel electrode (a first ITO layer), source/drain electrodes (SD), a passivation layer (PVX) and a common electrode (a second ITO layer); and the sequence of deposition and etching of an HFFS LCD manufactured by using five-photolithography method may include: a gate line and the gate electrode, the gate insulation layer, an active layer, source/drain electrodes, a pixel electrode, a passivation layer, and a common electrode.
The common electrode in an HFFS LCD has slits and thus has a larger resistance than a complete piece of plate common electrode flat, so RC signal delay of the common electrode is much larger, which causes the loading ability of the common voltage signal to decrease, thereby the crosstalk phenomena is more apparent and the picture quality is affected disadvantageously.